Thunderbolt ultra-high-speed interface technology and its measurement method

1. Introduction to Thunderbolt Ultra High-Speed ​​Interface

On February 24, 2011, local time in the United States, Intel officially released the Intel Labs product code-named "Light Peak" technology that has been promoted for several months.

Figure 1 ThunderBolt ultra-high-speed interface

Thunderbolt is a product of cooperation between Apple and Intel. It was developed by Intel and brought to the market through technical cooperation with Apple. This technology is mainly used to connect PCs and other devices. It combines two mature technologies, PCI Express data transmission technology and DisplayPort display technology. Two channels can transmit data of these two protocols at the same time. Each channel provides a bidirectional bandwidth of 10.3125Gbps. In order to reduce costs, Thunderbolt currently uses a copper core connection instead of the optical fiber link demonstrated earlier. Theoretically, the maximum transmission rate can reach 50Gbps, but it is currently set at only 10Gbps, leaving a lot of room for development.

2. Thunderbolt working principle and performance

Thunderbolt ultra-high-speed connection technology integrates PCI Express data transmission technology and DisplayPort display technology. It is driven by an Intel dedicated control chip and connected to the system chipset via PCI Express 2.0 x4 and DisplayPort 1.2 buses. PCI Express is used for data transmission, while DisplayPort is used for display signal transmission. It can also be connected directly to Intel processors.The integrated graphics core performs DisplayPort display output. The Thunderbolt control chip is essential to the system. But Intel said that its hardware does not require Intel's processor and chipset to work together. It is more like a micro routing switch., can quickly switch between data in two bidirectional channels.

Figure 2 Working principle of ThunderBolt

Thunderbolt uses a dedicated interface. The physical appearance of this interface is the same as the original Mini DsiplayPort interface, which is suitable for various light and small devices. It is compatible with display devices with DisplayPort interface, monitors with Mini DP interface, and adapters from Mini DP to HDMI/DVI/VGA and other interfaces. They can all be used normally on the Thunderbolt interface, and can transmit 1080p or even ultra-high-definition video and up to eight-channel audio.

Thunderbolt is backwards or forwards compatible depending on the cable used. Backwards compatible with PCI Express 2.0I/O control system, but IntelThere is no comment on USB 3.0. As for forward compatibility, the newer the better. You can find that the new port on the Macbook Pro is ready for optical transmission, which is more cost-effective.

In terms of device connection, Thunderbolt technology supports connecting 7 devices together in daisy chain form (that is, Apple says the MacBook Pro can connect 6 peripherals in series, including up to 2 Full HD DisplayPort display outputs), but requires that the DisplayPort 1.1 device must be at the end of the link.

In order to reduce costs, Thunderbolt currently uses a copper core connection instead of the fiber optic link demonstrated earlier, and the copper cable length is limited to 3 meters. Fiber optic cable products will also be launched later this year. However, copper cables will still retain an advantage in the future, that is, they can provide 10W power supply through the cable, while fiber optic Thunderbolt will not provide power supply function.

Figure 3 Comparison of transmission rates of various interfaces

3. Current uses of Thunderbolt

When Apple released the new MacBook Pro with Thunderbolt interface, many brands announced that they would launch Thunderbolt related products, including Aja, Apogee, Avid and Blackmagic. In terms of third-party support, Intel said that Western Digital and LaCie will both provide mobile hard disks compatible with Thunderbolt interface. Among them, LaCie has demonstrated a device using Thunderbolt, a dual SSD storage device for Raid. Of course, due to storage limitations, the combat effectiveness of Thunderbolt is really difficult to reflect in home use.

Such speed is too luxurious for home use, and the three-meter line length also greatly limits its scope of use. The current possible applications I can think of are:

* Multi-monitor support. Since you can connect 6 devices to a single port, theoretically, you can organize a 7-screen work platform.　

* Ultra-high-speed disk array, by setting up Raid with SSD and cooperating with Thunderbolt, you can get extremely exaggerated disk performance, which will be beneficial for professional work such as graphics processing and image rendering. 　　

Of course, as the technology becomes more popular and a large number of peripherals emerge, Thunderbolt's ultra-high transmission speed and single-interface multi-device capabilities will gradually demonstrate its advantages. After the emergence of optical fiber connections, with a single Mac machine as the computing core and a large number of related peripherals, it seems that a centralized processing environment can be arranged. By next year, everyone can start to update their current home network..

Figure 4 Early LightPeak used optical cables

Interface, also supports the PCI Express interface used by hard drives and other devices. Supporting PCI means that it is very easy to develop adapters for other interfaces, such as Thunderbolt and Ethernet converters, or Thunderbolt and Firewire converters, etc.

Thunderbolt will attract support from media production companies and professionals, including professional audio and video editing softwareMany companies, including manufacturer Avid, have become the first to support this technology. It is also worth noting that Thunderbolt cannot bring about a revolution in video itself. There are many bottlenecks that affect video quality, including graphics processors and operating systems.Once you want to upload videos to the Internet, bandwidth speed will also become a problem. But think back to the rise of MP3 in the 1990s: portable MP3 playersThe music storage was short-lived, the sound quality was poor, the production and playback software was ineffective, and the music could only be uploaded and downloaded using slow dial-up networks.As companies gradually improved it, bandwidth began to increase. Today, almost everyone who owns a computer uses it to store, transfer and play music. Computer music has become mainstream. So five years later, it is easy to imagine that when users make, copy and exchange large amounts of video files, they will also have the same convenience as audio files. Thunderbolt is not a sufficient condition, but it does eliminate a major bottleneck. At least for now, Thunderbolt is not a necessary interface, because there are currently almost no devices that can use this interface, but in the long run, Thunderbolt will definitely reduce a lot of troubles for users in the future, because Thunderbolt can replace almost all expansion interfaces.

5. Overview of Thunderbolt test methods

Figure 5 Overview of Thunderbolt test methods

The Thunderbolt signal rate is as high as 10.3125Gbps. Physical layer testing is one of the key links in product development and production. Physical layer consistency testing mainly includes three aspects:

1) Tx signal quality measurement, which only needs to measure the waveform parameters of the signal, such as eye diagram, jitter, edge time, amplitude, etc.;
2) Rx receiving performance measurement, which mainly measures the receiving voltage sensitivity, jitter tolerance, positive and negative signal time deviation tolerance, etc. of the receiving end;
3) Cable performance test, which mainly measures the differential impedance, insertion loss, crosstalk, etc. of the cable.

6. Thunderbolt Tx signal quality measurement

Figure 6 Thunderbold Tx conformance test points

The Thunderbolt compliance test point is shown in Figure 6, which is usually at the mDP connector. The compliance test requires the oscilloscope bandwidth to be at least 16GHz. Considering more accurate measurement and characterization, the recommended oscilloscope bandwidth is 25GHz. The oscilloscope is required to have a de-embedding function to remove the influence of the test fixture. The test fixture used is shown in Figure 7.